The present invention relates to a hydraulic pressure booster which is used to perform servo control of input and output at the preset servo ratio and is used in a brake booster or the like, and it particularly relates to a hydraulic pressure booster, which is designed to reduce the loss stroke of an input shaft in the initial stage of the operation.
In general, a hydraulic pressure booster consists of a power piston slidably engaged with the housing thereof, a power chamber, into which hydraulic pressure acting on one end of said power piston is introduced, a control valve to control and change over the communication between said power chamber and the hydraulic pressure source or reservoir, an input shaft to operate said control valve, and an output shaft connected with said power piston. By changing over the control valve through the operation of input shaft, hydraulic pressure from a hydraulic pressure source is introduced into the power chamber, and the power piston is operated by this hydraulic pressure to output the power from the output shaft. In such a case, the hydraulic pressure booster performs the so-called servo control, by which the output from the output shaft is controlled according to the input of the input shaft.
In such a hydraulic pressure booster, it is necessary to enlarge the area of the passage of the control valve communicating the hydraulic pressure source and the power chamber during operation and to expand the area of the passage of the control valve for the communication between the power chamber and reservoir when operation is released. In both cases, the opening of the control valve must be increased. However, if the opening of the control valve is increased, the displacement of the input shaft is increased, and much time is required from the initiation of the operation to the changeover of the passage of control valve. In other words, the loss stroke of the input shaft is increased in the initial stage of the operation.
In this respect, a hydraulic pressure booster was proposed in the U.S. Pat. No. 4,656,923, in which the responsiveness was improved by reducing the loss stroke of the input shaft.
In the hydraulic pressure booster described in this publication, the opening of the control valve is increased by extending the relative displacement of the power piston and the input shaft when the operation is released. During non-operation, the input shaft is maintained at the position advanced forward in relation to the power piston by a stopper means in order to bring the input shaft closer to the control valve. By this hydraulic pressure booster, the control valve is changed over immediately at the starting of the operation and the fluid is introduced into the power chamber and the power piston is quickly operated because input shaft is located very close to the control valve. When the operation is released, the fluid in power chamber is quickly discharged to the reservoir, and the power piston is quickly returned because the opening of the control valve is increased.
In order to control the backward movement of the input shaft in relation to the power piston, a detent is provided movable forward and backward in relation to the power piston so that the detent can be moved forth toward the control valve by the stopper means together with the input shaft during non-operation.
However, the degree of mounting freedom of such a detent is limited because it must positively hinder the input shaft from coming out of the power piston. When the degree of mounting freedom is limited in this way, the detent may not move positively. The lack of the positive movement of the detent may mean that the input shaft cannot be moved forward in relation to the power piston when the input shaft is not operated. This causes the problem that the loss stroke of the input shaft cannot be reduced.
If free movement is assured to actualize the positive movement of the detent, a new problem arises that the detent is separated from the power piston and loses its detent function.